The invention relates generally to seals for gas drying systems having a tank which contains pressurized gas, and more particularly, to a seal which holds an elongate antenna at an opening of the pressurized tank in a gas drying system which utilizes microwave energy for the regeneration of desiccant contained in the tank.
Drying devices which receive a wet gas under pressure such as air containing a high level of moisture are well known. These gas drying devices are commonly used in many industrial applications such as spray painting, pneumatic control systems and air operated equipment. It is also known in such devices to utilize a desiccant such as activated alumina, carbons, silica gels or molecular sieves located in a tank to adsorb and remove the moisture from the wet air which is inserted under pressure at an inlet and is carried to another end of the tank. Such air drying devices frequently use a portion of the dried air also called a purge gas from one desiccant tank or chamber that is drying air to regenerate the desiccant in another tank that has already removed moisture from the wet air earlier.
These known regenerative dryers (either heated or heatless) use a dual tank or dual chamber system in which wet gas is received through an inlet at the top of one of the tanks. One tank performs a gas drying function while another tank of the system operates to regenerate previously saturated desiccant. The dual chamber/tank systems have both tanks interconnected with each other. Additionally, both tanks are interdependent in that the tanks both work together to shift between regenerative and gas drying cycles. Once the desiccant in one tank drying the wet gas is sufficiently saturated during the gas drying cycle and the desiccant in the other tank is dried out during the regeneration cycle, the cycles are reversed by flipping diverter valves interposed between the two tanks. Dry purge gas received from the other tank drying wet air is, in turn, used to dry and regenerate the saturated desiccant in the one tank. These drying systems are cycled back and forth requiring the use of two tanks to dry out the wet gases and regenerate desiccant.
Certain gas drying systems use microwave energy to activate and regenerate the desiccant material in the tank. A microwave generating device, such as magnetron, is used to generate microwaves which are carried within a waveguide to an antenna disposed within the waveguide. The microwaves are carried along the length of the antenna which extends through an opening and into the tank. The microwave energy transmitted via the antenna, that is partially immersed in the desiccant, is used to regenerate the saturated desiccant within the tank.
In these tanks which utilize microwave energy for desiccant regeneration, an insulative bushing member positioned through an opening of the tank has been used in an effort to hold the antenna in place. Disadvantageously, at times the antenna has slipped out of its initially set position upon pressurization/depressurization of the tank during gas drying and desiccant regeneration cycles. Such movement of the antenna can occur especially during changeover from the regeneration cycle to the gas drying cycle in which the tank operates at 25-400 (generally 100-200) pounds per square inch (psi). It has been found that when the pressure is lowered in the tank the antenna has a tendency to move down into the tank and when the tank is highly pressurized (during the drying cycle) the antenna and the insulative bushing member have a tendency to move up (or even out) toward the exterior of the tank. Movement of the antenna from its originally set position can also cause arcing and/or poor energy transfer when utilizing microwave energy for desiccant regeneration. Disadvantageously, arcing can cause significant temperature increases which may result in melting of a bushing member. Accordingly, there is a need for a seal for pressurized gas drying tanks which reduces the affects of arcing while adequately maintaining the position of a microwave antenna during gas drying and desiccant regeneration cycles.
One or more of the problems noted above are solved in accordance with the present invention by a seal for holding in place an antenna which passes through an opening of a pressurized tank containing desiccant material. In one aspect of the invention, the seal arrangement uses a shaped insulator to transition the impedance of the microwaves. A mechanical arrangement is provided to prevent the pressure inside the tank from pushing the seal out through the tank opening. Alternative embodiments involve channel and tab snap together components. The invention allows for simple assembly which limits microwave losses while retaining the relative positioning of the antenna and seal components with or without positive pressure inside the tank.